Reference signals in cellular communication networks

Abstract

For transmission of tracking reference signals in a cellular network a periodic set of transmission occasions is defined. A window is also defined in relation to at least one paging occasion, wherein the base station does not transmit tracking reference signals outside of the window. The base station also transmits an indication of active transmission occasions within the window and only transmits tracking reference signals in active transmission occasions.

1 . A method of configuring tracking reference signals in a cellular communications system for use while a UE is in idle mode, the method performed by a base station and comprising the steps of:
 defining at least one tracking reference signal configuration comprising periodic transmission occasions for tracking reference signals;   defining a tracking reference signal window in relation to at least one paging occasion, wherein the base station only transmits tracking reference signals in transmission occasions which are within the window;   transmitting an indication of active transmission occasions within the tracking reference signal window in which the base station will transmit tracking reference signals; and   transmitting tracking reference signals in the active transmission occasions.   
     
     
         2 . The method of  claim 1 , wherein
 the indication of active transmission occasions comprises a bitmap.   
     
     
         3 . The method  claim 2 , wherein
 bits of the bitmap correspond to transmission occasions and indicate whether the transmission occasion is active.   
     
     
         4 . The method of  claim 1 , wherein
 the periodic transmission occasions have a period of 10, 20, 40, or 80 ms.   
     
     
         5 . The method of  claim 1 , wherein
 the window spans at least a period between a paging indication corresponding to the paging occasion and the paging occasion.   
     
     
         6 . The method of  claim 1  wherein
 the at least one tracking reference signal configuration is specific for use while UEs are in idle mode. 
 
     
     
         7 . The method of  claim 1 , wherein
 the at least one tracking reference signal configuration is transmitted in RRC signalling.   
     
     
         8 . The method of  claim 7 , wherein
 the at least one tracking reference signal configuration is transmitted in a system information block transmission.   
     
     
         9 . The method of  claim 1 , wherein
 the at least one tracking reference signal configuration is cell specific or paging occasion specific.   
     
     
         10 . The method of  claim 1 , wherein
 the active transmission occasions include at least one occasion prior to a paging indication.   
     
     
         11 . The method of  claim 1  wherein
 the active transmission occasions apply to a group of UEs which are active for a particular paging occasion. 
 
     
     
         12 . The method of  claim 1 , wherein
 the indication of active transmission occasions comprises a sequence transmitted as a paging indication.   
     
     
         13 . The method of  claim 12 , wherein
 each sequence corresponds to a set of active transmission occasions.   
     
     
         14 . The method of  claim 1 , wherein
 the indication of active transmission occasions comprises timing of a paging indication relative to a related paging occasion in at least one paging occasion.   
     
     
         15 . The method of  claim 1 , wherein
 indication of active transmission occasions is transmitted in RRC signalling.   
     
     
         16 . The method of  claim 1 , further comprising:
 transmitting an indication of a tracking reference signal configuration of the defined at least one tracking reference signal configurations which is enabled for a UE to which the indication is transmitted.   
     
     
         17 . The method of  claim 16 , wherein
 the indication is transmitted as a bitmap in which each bit corresponds to a tracking reference signal configuration.